This deal: https://www.ozbargain.com.au/node/675872 - is back for 2023. The comments section on that thread are full of good information.
These are the courses you can do:
Diploma of Dementia Care
Diploma of Sustainable Living
Undergraduate Certificate in Sustainable Living
Undergraduate Certificate in Data and Environmental Management
Undergraduate Certificate in Antarctic and Climate Science
Graduate Certificate in Tourism, Environmental and Cultural Heritage
Generally speaking you get 4 subjects fee free (4 subjects = certificate). Accordingly if you do a diploma (8 subjects = diploma) you need to pay for subjects 5-8.
Long story short - it's fee free (to you) if you are entitled to a commonwealth supported place (ie the uni still bills the government for ~50% of what the total fee would ordinarily be - and then waives the other 50% which you would ordinarily have to pay (or put on HECS) if they weren't offering a fee waiver)). If you aren't eligible for a commonwealth supported place you are toast. As a rule of thumb as long as you are an Australian or NZ citizen, live in Australia and haven't had more than 7 years of commonwealth supported study you will probably be eligible for a commonwealth supported place (but check the criteria yourself).
If you pick your subjects carefully you can do it all online. Some courses have optional online tutorials (various times - including outside work hours) - I turned up to one this semester and it was a complete waste of time so haven't bothered again. I've just submitted my final assignments for 2 subjects in the certificate of sustainable living (which I signed up to as a result of the 2022 post and comments). I'm enrolled for 2 more subjects to finish off the certificate starting tomorrow. I was planning on 'upgrading' to the diploma for 2023 (and paying for subjects 5-8) … but now that this deal is back I'll probably just enroll in the Antarctic and Climate Science certificate instead.
There is some really great info in the comments to the 2022 deal thread which you should read if you are interested.
Have just the other day submitted my last assignment in diploma of dementia care. The 2 neuro subjects were a bit harder but other than that, pretty easy going for most of the course. Had a few times where i needed extensions due to being ill, family issues etc, and they were always very understanding. If it interests you at all, I definitely recommend giving it a go.